This disclosure relates to optimized integrated controls for an oxy-fuel combustion power plant. In particular, this disclosure relates to optimized integrated controls for an oxy-fuel pulverized coal power plant or an oxy-fuel circulating fluidized bed power plant.
Oxy-fuel combustion systems use oxygen instead of air for combustion of the primary fuel to produce a flue gas that comprises mainly water vapor and carbon dioxide. This results in a flue gas with carbon dioxide concentrations that are greater than 80 volume percent. While two thirds of the flue gas is recycled within the system, the remaining portion (consisting mainly of carbon dioxide and water vapor and small quantities of argon, nitrogen, nitrogen oxides, and sulfur oxides) is cleaned up, compressed and later transported to storage or to other applications.
The FIG. 1 depicts an exemplary power plant 100 configured to permit oxy-firing. The power plant 100 generally comprises an air separation unit 200, a boiler 300 and a flue gas treatment system 400. The air separation unit 200 is in fluid communication with the boiler 300 and the flue gas treatment system 400. The boiler 300 and the flue gas treatment system 400 lie downstream of the air separation unit, with the flue gas treatment system 400 lying downstream of the boiler 300. The air separation unit 200 separates outside air from nitrogen and delivers gas rich in oxygen to the boiler 300. The boiler 300 is in communication with a steam turbine 302 and supplies steam to the turbine 302 to drive it. Flue gases from the boiler 300 are discharged to a flue gas dryer 304 and to an electrostatic precipitator 306.
A portion of the dried and particulate-free flue gas that emanates from the electrostatic precipitator 306 is recycled to the boiler 300, where it is mixed with additional incoming air (that is rich of oxygen and free of nitrogen) and delivered to the boiler 300. The remaining portion of the flue gases (which are rich in carbon dioxide) that are not recycled are further treated to remove moisture and are then subjected to compression in a compressor 308 and sequestration in a sequestration facility 310.
There are a number of new challenging issues associated with deploying oxy-fuel combustion in a power plant. Some of these problems are listed below.
The use of oxy-fuel combustion systems in a power plant to enable the easier capture of carbon dioxide results in additional energy consumption over comparative power plants that do not use oxy-fuel combustion. This additional energy consumption occurs primarily from energy consumption in the air separation unit (about 25 to about 30%) and from the flue gas recirculation (about 5 to about 10%). This increase in energy consumption results in a reduced output from the power plant.
As a result of using gas that is rich in oxygen, there is a change in combustion that occurs when the ratio of oxygen to the recycled-flue gas ratio is changed. This provides new challenges for controlling the power plant.
External disturbances to the plant system such as changes in the electric load demands or in carbon dioxide production will affect the air separation unit 200, the boiler 300 and the flue gas treatment system 400. Since the recycling of flue gases and the closed loop control of the power plant are interlinked with changes in the electric load demands or with carbon dioxide production, these changes cause changes to the functioning of the air separation unit 200, the boiler 300 and the flue gas treatment system 400.
In order to improve the efficiency of the functioning of the plant and in order to minimize the effect of changes in the electric load demands or the changes in carbon dioxide production, it is desirable to use control systems that can act in cooperation to improve energy generation while at the same time improving carbon dioxide sequestration.